Reference counting garbage collection

[Tim Peters]

[Paul Rubin, presumably asking about word-addressed machines]
> What machines are those anyway?

Generally high-performance number-crunchers, like several flavors of Cray
and the original Alphas.

> How do they deal with byte arrays?

Painfully.  Here's a paper about Alphas:

   http://www.research.compaq.com/wrl/DECarchives/DTJ/DTJO08/DTJO08SC.TXT

When C was first implemented on Crays, "byte arrays" were purely a software
fiction.  By convention, we stored a 3-bit byte offset (64-bit words were
the smallest addressable unit) in the *high*-order bits of a pointer.  The
compiler then generated oceans of shift and mask operations accordingly.
short, int and long were all 64 bits.  This was a good test to see whether
programmers had read the C std <wink>.